The move comes amid growing calls from members of the Convention on the future of Europe for a pan-EU referendum to approve the constitution.

A Union-wide poll would be a way of politically reconnecting the EU and its citizens, Iñigo Méndez de Vigo, a member of the Convention’s praesidium, told this paper.

But forum insiders warn that political and legal obstacles may prevent other member states, such as Germany, from holding referenda. In addition, a decision to hold such polls across the EU could throw up a crucial question: would such referenda be deemed carried if an overall majority of European citizens were in favour or, instead, if a majority of the population in each EU country voted ‘yes’.

The first scenario is widely held as being unrealistic as it implies that even if, for example, a majority of Irish or Spaniards voted against the constitution, they would still be subject to it if, on average, more Europeans voted ‘yes’ than ‘no’.

The latter option, with individual referenda organised at the same time in each EU member state, is seen as more acceptable. Méndez de Vigo believes that an EU-wide referendum would be key to the future constitution winning broad political acceptance and, therefore “lasting”.

“If this constitution is written with the ambition of lasting for 50 years – as [Convention President] Giscard says – we should put it for approval through referenda.

“The EU should finish with revisions of its system every five years. You can’t pressurise 25 governments to go through changes every five years.”

Spain will be the first country to announce a vote on the constitution at the same time as elections for the European Parliament.

France, Portugal, Denmark and Ireland have already hinted they will each hold a referendum, but failed to link it to the European polls.

Méndez de Vigo admits that organising a pan-European referendum may be problematic: “Germans are allergic to referenda, due to historical reasons,” he said, adding however that “this is a very special issue”.

Another problem is some countries’ reluctance to undertake popular consultation, fuelled by fears that citizens may reject the constitution.

“Some fear it [the constitution] will not be accepted. But isn’t it an even bigger failure to know that your people would have rejected it if you asked them to vote?” he commented. “If I were [British Prime Minister] Tony Blair, I would call a referendum on the constitution and on the euro on the same day. Because this is a package: ‘this is Europe, and you have to make a choice’.”

A negative result in such a poll would entail the withdrawal of the concerned country from the EU, he added.

Valéry Giscard d’Estaing suggested “consultation of Europeans at the occasion of elections for the European Parliament” when he opened the Convention on 28 February 2002.

However, he stopped short of using the word “referendum”.

According to Nikolaus Meyer-Landrut, the Convention’s spokesman, there are ways of consulting the public without resorting to a referendum.

“The European elections could be the occasion for Parliamentary candidates to campaign on the constitution, and their election could be seen as an implicit approval of the constitution.

“Alternatively, some member states could organise referenda,” he said.

A Convention insider warns that it would be an interference in EU states’ legal systems to decree that the constitution should be adopted by referenda.

“We cannot introduce an obligation for all member states to organise a referendum in June 2004,” he added.

Méndez de Vigo will open debate on the issue after the praesidium completes its intense work on drafting the constitution. “We will discuss the matter between June and the start of the Intergovernmental Conference,” the Spaniard added.